1. Field of the Disclosure
The present application relates to an organic light emitting display (OLED) device. More particularly, the present application relates to an OLED device adapted to enhance luminous images.
2. Description of the Related Art
Recently, a variety of flat panel display devices with reduced weight and volume corresponding to disadvantages of cathode ray tubes (CRTs) are being developed. The flat panel display devices include liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panels (PDPs), electroluminescence (EL) devices and so on.
The electroluminescence devices are classified into an inorganic light emitting display device and an OLED device on the basis of the formation material of an emission layer. Such electroluminescence devices have features such as high response time, high light emission efficiency, high brightness and wide viewing angle because of using self-illuminating elements.
The OLED device corresponding to one of the electroluminescence devices has features of high brightness and a low driving voltage. Also, the OLED device being a cell-luminous device can have a high contrast ratio and realize a large-sized thin display screen. Moreover, the OLED device is easy to realize motion images because of its response time of several micro-seconds (μs). Furthermore, the OLED device is not limited to the viewing angle, and maintains a stable state at a low temperature.
The OLED device includes array elements and organic light emitting diodes (or elements). The array element includes a switching thin film transistor connected to a gate line and a data line, and a driving transistor connected to the respective organic light emitting diode. The organic light emitting diode includes a firs electrode connected to the driving thin film transistor, and an organic emission layer and a second electrode stacked on the first electrode.
In an ordinary OLED device, the organic emission layer is generally formed through a thermal evaporation process using a shadow mask. A recently large-sized display device forces the shadow mask to severely sag. The sagging shadow mask causes depositing faults of the organic emission layer to be generated. Due to this, it is difficult to apply the shadow mask to a large-sized substrate.
In order to solve this problem, a print method using one of an ink-jet apparatus and a nozzle coating apparatus is proposed. The print method jets or injects a liquefied organic emission material into openings (or regions), which are defined by a bank pattern, using one of the ink-jet apparatus and the nozzle coating apparatus. The organic emission material must be ununiformly coated. Actually, the organic emission material starts to harden from the central region of the opening, and is solidified at a relatively slow speed in the central region of the opening compared to the edge regions of the opening and adjacent to the bank pattern. This phenomenon enables the organic emission material to harden in a state that a part of the organic emission material internally flows from the central region of the opening to the edge regions of the opening. In accordance therewith, the organic emission material is formed thicker in edge regions of the opening adjacent to the bank pattern, compared to the central region of the opening.
Due to this, an organic emission layer cannot have a planarized surface. Also, a part of the organic emission layer is formed thicker and developed darker than the other portion. The darkly developed portion is viewed to users like a stain. As such, the thick portion of the organic emission layer is treated in such a manner as to be not included a substantial emission region and viewed to users. This treatment of the organic emission layer deteriorates the aperture ratio of the OLED device,
To address this matter, a double layered bank pattern formation method is proposed which allows the entire surface of the organic emission layer including edges of the organic emission layer adjacent to the bank pattern to be planarized. The double layered bank pattern formation method forms a first bank pattern and a second bank pattern on the first bank pattern. However, although the double layered bank pattern is formed, the organic emission layer is formed thicker in edges of an active area compared to the central portion of the active area.